The present invention relates to a surface examining (or inspection) method and a surface examining (or inspection) apparatus, for examining or inspecting a state of a surface of an object to be measured, for example, a surface of a semiconductor wafer or the like.
As a conventional surface examining apparatus, for example, the apparatus disclosed in the Japanese Patent Application No. Tokugan-Hei 6-141118, or the like is known. In such a surface examining apparatus, an object to be measured is illuminated with a parallel light from an illuminating optical system, and then the state of a surface thereof is observed by passing the reflected light from the surface through an object-side telecentric optical system.
An object-side telecentric optical system has an advantage of setting the distance (distance to object) between a lens of an object-side telecentric optical system and a surface to be examined, of an object to be measured desirably. Therefore, in such a surface examining apparatus, an object-side telecentric optical system can be arranged more freely.
However, in such a surface examining apparatus, because a normal line of a surface to be examined coincides with an optical axis of an object-side telecentric optical system, there is a problem that a large-sized lens of an object-side telecentric optical system is required in order to observe the surface to be examined in a wide region. Further, there is another problem that the size of the surface examining apparatus is large in a direction normal to the surface to be examined. Such problems also occur in the case of using an image-object-side telecentric optical system instead of an object-side telecentric optical system.
The present invention was developed in view of the above-described problems. The present invention was completed on the basis of inventors"" study about a surface examining method and a surface examining apparatus, in which a large-sized lens of an object-side telecentric optical system is not required and which enables observation in a wide region on the surface to be examined.
That is, in accordance with one aspect of the present invention, the surface examining method for examining a surface of an object to be measured, by observing a light reflected from the object through an object-side telecentric optical system or an image-object-side telecentric optical system, comprises the steps of; arranging the object-side telecentric optical system or the image-object-side telecentric optical system so that an optical axis thereof is inclined with respect to a direction normal to the object to be measured, and observing the light reflected from the object to be measured.
In such a surface examining method, because the object-side telecentric optical system or the image-object-side telecentric optical system is arranged so that an optical axis thereof is inclined with respect to a direction normal to the object to be measured, it is possible to examine a wide region on the surface to be examined and to reduce the size of the apparatus for examining, in a direction normal to the surface to be examined.
In the surface examining method, it is preferable that the surface examining method further comprises the step of forming an image of the light issued from the object-side telecentric optical system or the image-object-side telecentric optical system at an image pickup part, wherein the image pickup part is inclined so as to coincide with an image plane in a paraxial domain.
In such a surface examining method, because the image pickup part is inclined in a direction in which a fading portion (vagueness) is cleared from the image, the fading portion can be corrected. As a result, the method enables highly reliable examination.
The illuminating light may be directed to the object to be measured in a direction which is different from that of an extended line of the optical axis of the object-side telecentric optical system or the image-object-side telecentric optical system.
In such a surface examining method, because the object to be measured is illuminated from a direction which is different from that of an extended line of the optical axis of the object-side telecentric optical system or the image-object-side telecentric optical system, a half mirror is not required. As a result, it is possible to have no effect of a ghost caused by the half mirror on the image and to prevent reduction of the amount of light which might be caused by using the half mirror. Further, because the half mirror is not required, the cost of the surface examining apparatus can be decreased.
In accordance with another aspect of the present invention, the surface examining method for examining a surface condition of an object to be measured by observing a light reflected from the object through an object-side telecentric optical system, comprises the steps of; arranging the object-side telecentric optical system so that an optical axis thereof is inclined with respect to a direction normal to the object to be measured, forming an air image corresponding to a surface to be examined, of the object to be measured by using the object-side telecentric optical system, and observing the air image.
In such a surface examining method, the air image is observed by a predetermined optical system. In the case of a construction of the optical system, preferably, optical parts are suitably chosen and arranged to eliminate the effect of far and near distances from the object on the image to be observed. As a result, the correction of the unbalanced state of the image, which might be caused by the far and near distances from the object is not required in the step of an image processing.
In accordance with another aspect of the present invention, the surface examining method for examining a surface condition of an object to be measured by observing a light reflected from the object through an object-side telecentric optical system, comprises the steps of; arranging the object-side telecentric optical system so that an optical axis thereof is inclined with respect to a direction normal to the object to be measured, forming an image corresponding to a surface to be examined, of the object to be measured on a ground glass by using the object-side telecentric optical system, and observing the image.
In such a surface examining method, the formed image on the ground glass is observed through a predetermined optical system. In the case of a construction of the optical system, preferably, optical parts are suitably chosen and arranged to eliminate the effect of far and near distances from the object on the image to be observed. As a result, the correction of the unbalanced state of the image, which might be caused by the far and near distances from the object is not required in the step of an image processing.
When the surface of the object to be measured is examined, the object to be measured may be rotated in parallel with the surface to be examined, that is, around the normal of the surface to be examined, of the object to be measured.
In accordance with another aspect of the present invention, in the surface examining apparatus for examining a surface condition of an object to be measured, by observing a light reflected from the object through an object-side telecentric optical system or an image-object-side telecentric optical system, the object-side telecentric optical system or the image-object-side telecentric optical system is arranged so that an optical axis thereof is inclined at a predetermined angle with respect to a direction normal to the object to be measured.
In such a surface examining apparatus, because the object-side telecentric optical system or the image-object-side telecentric optical system is arranged so that an optical axis thereof is inclined with respect to a direction normal to the object to be measured, it is possible to examine a wide region on the surface to be examined and to reduce the size of the apparatus for examining, in a direction normal to the surface to be examined.
It is preferable that the surface examining apparatus further comprises an image pickup part at which an image of the light issued from the object-side telecentric optical system or the image-object-side telecentric optical system is formed, wherein the image pickup part is inclined so as to coincide with an image plane in a paraxial domain.
In such a surface examining apparatus, because the image pickup part is inclined in a direction in which a fading portion (vagueness) is cleared from the image, the fading portion can be corrected. As a result, the apparatus enables highly reliable examination.
In accordance with another aspect of the present invention, in the surface examining apparatus for examining a surface condition of an object to be measured, by observing a light reflected from the object through an object-side telecentric optical system or an image-object-side telecentric optical system, the object-side telecentric optical system or the image-object-side telecentric optical system is arranged so that an optical axis thereof can be inclined at a predetermined angle with respect to a direction normal to the object to be measured.
In such a surface examining apparatus, because the object-side telecentric optical system or the image-object-side telecentric optical system is constructed so that an optical axis thereof can be inclined at a predetermined angle with respect to a direction normal to the object to be measured in case of necessity, it is possible to examine a wide region on the surface to be examined. On the other hand, it is also convenient that the object-side telecentric optical system or the image-object-side telecentric optical system is arranged so that the optical axis can coincide with the direction normal to the object to be measured.
It is preferable that the surface examining apparatus comprises an image pickup part at which an image of the light issued from the object-side telecentric optical system or the image-object side telecentric optical system is formed, wherein the image pickup part can be inclined so as to coincide with an image plane in a paraxial domain.
In such a surface examining apparatus, because the image pickup part can be inclined in a direction in which a fading portion is cleared from the image in case of necessity, the fading portion can be corrected. As a result, the apparatus enables highly reliable examination.
The surface examining apparatus may comprise a ground glass instead of the image pickup part.
In such a surface examining apparatus, because an air image is formed and observed, the unbalanced state of the image, which might be caused by the far and near distances from the object can be cleared from the image to be observed optically without an image processing. Further, because the image is formed on the ground glass, it is easy to focus the image formed on the ground glass.
The surface examining apparatus may further comprise a mirror for illuminating the object to be measured in a direction which is different from that of an extended line of the optical axis of the optical system. Further, the number of the mirrors may be not less than two, wherein the mirrors are arranged to illuminate the object to be measured in a direction which is different in directions from that of one another.
The surface examining apparatus may further comprise a rotating device for rotating the object to be measured in parallel with the surface to be examined, of the object to be measured.